Thin-film display panels (such as LCD or electroluminescent) have been known to be very useful for displaying information as the thin-film structures including the cross electrodes and contact pads, can be deposited on a glass substrate thereby providing a matrix display panel capable of being selectively energized to activate individual pixels thereon. One of the problems encountered in the manufacture of thin film display panels is the development of processes that pattern the thin film electrode structures while in an in-line deposition system.
Most thin-film devices have had their thin-film structures patterned either by a wet process known as photolithography or by shadow masking. Photolithography is very similar to processes used to develop photographs in that the deposit to be patterned is coated with light-sensitive material, which is then exposed to a negative or positive pattern and then developed and later stripped in various corrosive developing solutions. The disadvantages of this method is that it is slow and labor intensive, and involves many steps, each one subject to failure or possible contamination of the thin-film device.
With respect to the use of shadow masking to deposit thin-film structures, reference is made to U.S. Pat. No. 4,335,161 to Fang C. Luo, entitled "Thin-Film Transistors, Thin-Film Transistor Arrays and a Process for Preparing the Same". In summary, the Luo patent appears to disclose a method of preparing a thin-film transistor or an array of thin-film transistors by depositing in vacuum the different components through a single apertured mask, wherein the apertured mask is moved in predetermined pattern for the deposition of each of the components. In Luo, once the deposition of the different structures is complete, the assembly that is formed is then removed from the vacuum and the fabrication completed by techniques such as photolithography.
As in Luo, shadow masking is usually performed over small substrates with stiff masks that are manually clamped to ensure even contact with a particular substrate. This is a relatively slow process and usually requires breaking vacuum in the deposition chamber, resulting in some thin-film contamination. When depositing through a large area mask, it is common that the substrate is not perfectly flat or not level with respect to its surrounding substrate holder. The present invention addresses the problem arising from the difficulties of remote automatic handling of large area shadow masks in an in-line deposition system.
With respect to the use of photolithography, thin-film patterns have typically been aligned to the substrate and each other by optical means and the substrate is moved manually into position with the aid of a micromanipulator or an optical scanner which provides information to a computer which performs a similar function. The aligned substrate is then exposed and wet processed to achieve the desired pattern. In contrast, most shadow masking processes are aligned manually by dropping the masks over pins located on a substrate carrier. Therefore, an apparatus which is effective for remotely operating automatic masking systems where there is a need to eliminate the need for breaking vacuum, which would contaminate deposit of thin films, would be considered an advancement in the art.